This invention relates generally to liquid vapor phase separation and, more particularly, to the separation of a two-phase refrigeration flow into a liquid phase portion and a vapor phase portion in a refrigerant vapor compression system having a flash tank economizer and operating in a transcritical cycle.
Refrigerant vapor compression systems are well known in the art and commonly used in mobile refrigeration systems, such as transport refrigeration systems for refrigerating air or other gaseous fluid supplied to a temperature controlled cargo space of a truck, trailer, container or the like for transporting perishable items, fresh or frozen, by truck, rail, ship or intermodal.
Conventional refrigerant vapor compression systems used in transport refrigeration applications typically include a compressor, a refrigerant heat rejection heat exchanger, and a refrigerant heat absorption heat exchanger arranged in a closed loop refrigerant circuit. An expansion device, commonly an expansion valve, disposed in the refrigerant circuit upstream, with respect to refrigerant flow, of the refrigerant heat absorption heat exchanger and downstream of the refrigerant heat rejection heat exchanger. These basic refrigerant vapor compression system components are interconnected by refrigerant lines and are arranged in accord with known refrigerant vapor compression cycles. Refrigerant vapor compression systems may be operated in either a subcritical pressure regime or a transcritical pressure regime depending upon the particular refrigerant in use.
Refrigerant vapor compression systems operating in the subcritical regime are commonly charged with fluorocarbon refrigerants such as, but not limited to, hydrochlorofluorocarbons (HCFCs), such as R22, and more commonly hydrofluorocarbons (HFCs), such as R134a, R410A, R404A and R407C. In refrigerant vapor compression systems operating in a subcritical cycle, both the refrigerant heat rejection heat exchanger, which functions as a refrigerant vapor condenser, and the refrigerant heat absorption heat exchanger, which functions as a refrigerant liquid evaporator, operate at refrigerant temperatures and pressures below the refrigerant's critical point.
However, interest is being shown in “natural” refrigerants, such as carbon dioxide, for use in air conditioning and transport refrigeration systems instead of HFC refrigerants. Because carbon dioxide has a low critical temperature and a low liquid phase density to vapor phase density ratio, most refrigerant vapor compression systems charged with carbon dioxide as the refrigerant are designed for operation in the transcritical pressure regime. In refrigerant vapor compression systems operating in a transcritical cycle, the refrigerant heat rejection heat exchanger, which functions as a refrigerant vapor cooler rather than a refrigerant vapor condenser, operates at a refrigerant temperature and pressure in excess of the refrigerant's critical point, while the refrigerant heat absorption heat exchanger, which functions as a refrigerant evaporator, operates at a refrigerant temperature and pressure in the subcritical range.
It is also known practice to incorporate an economizer circuit into the refrigerant circuit so that the refrigerant vapor compression system may be selectively operated in an economized mode to increase the capacity of the refrigerant vapor compression system. In some refrigerant vapor compression systems operating in a transcritical mode, the economizer circuit includes a flash tank incorporated into the refrigerant circuit between the gas cooler and the evaporator. In such case, the refrigerant vapor leaving the gas cooler is expanded through an expansion device, such as a thermostatic expansion valve or an electronic expansion valve, prior to entering the flash tank wherein the expanded refrigerant separates into a liquid refrigerant component and a vapor refrigerant component. The vapor component of the refrigerant is thence directed from the flash tank into an intermediate pressure stage of the compression process. The liquid component of the refrigerant is directed from the flash tank through the system's main expansion valve prior to entering the evaporator. U.S. Pat. No. 6,385,980 discloses a transcritical refrigerant vapor compression system incorporating a flash tank economizer in the refrigerant circuit between the gas cooler and the evaporator.
Being mobile, transport refrigerant vapor compression systems are subject to vibration and movements not experienced by stationary refrigerant vapor compression systems. Transport refrigeration systems are also subject to size restrictions due to limitations on available space and weight considerations due to fuel economy not generally associated with stationary refrigerant vapor compression systems, such as air conditioners and heat pumps. Accordingly, a desire exists for phase separation apparatus that is easy to manufacture, compact and lightweight, yet structurally durable in a mobile refrigeration systems environment and at refrigerant pressures associated with application in a refrigerant vapor compression system operating in a transcritical pressure regime.